Photovoltaic device



Feb. 10, 1959'" E. s. RITTNER 2,873,303 ruo'rovouruc DEVICE FiledNov. 1. 1954 ALUMINUM ANTIMONIDE METAL COATING\ y. I v 1 SOLAR ENERGY 3a 2 j I ANTl-REFLECTNG COATING METAL COATING\5 7 E r I g/ SOLAR ENERGY fa; 9 3 v 'I A!" 2 INVENTOR EDMUND S. RITTNER AGENT United States "PatentPHOTOVOLTAIC DEVICE Edmund S. Rlttner, White Plains, N.Y., ualgnor toNorth Amerlcanl'hlllps (Iompany, Inc, New York, N. Y., a corporationofDelaware "Application November 1,1954, Serial No. 466,010

4 Claims. ((11. 136-89) My invention relates to devices capableoigenerating electric 'currents in response to the impinging thereon ofradiation in the visibleregion of the spectrum.

Ascmyinvention isparticularly useful-in connection with the conversionof solar energy, I shalldcscribe the same in this connection. However,the invention'extends to other types ofphotosensitive devices, such asexposure metersfor' photographic use :and photo-electric cells.

It has recently been proposed to convert solar'radiation into electricalpower by means of asilicon p-n junction photocellformed of athin layerofp-type silicon onan' n-type base. While such photocells have a muchhigher efiicicncy for solarenergyyconversion than photovoltaic cellspreviously available, the eiiiciency is still below the desiredxvalue. ii

The .main object of my invention is to increase the "efficiency ofsuchdevices and I have found it possible to achieve this vpurposebyemployingaluminum antimonide instead o'fthematerials previously used,which materials inadditionto silicon include germanium, cadmium sul-:phide, selenium and cuprous oxide.

Invaccordance with my invention, I form the photovoltaic cell 'o'f twoportions of aluminum antimonide (AlSh) in intimate contact; meet theportionsbeing ofp-type andthe other being of n-type material. Oneofthese portions, which has a surface adapted to'receive the'radiation,isgiven a thickness smaller than the minoritycarrierdifiusionlength.

In order that the inventionmay be clearly understood and readily carriedinto efiect, I shall describe the same .in more detail with reference tothe accompanying drawing, in which:

Figure 1 shows in section a 'p-n junction photovoltaic deviceaccordingto the invention with anrappropriate load I circuit, and lFig.2 is a sectional view of another embodiment of the invention.

Thephotovoltaicfidevice shown in Fig. l, which may 2 serve to convertsolar radiation into electrical energy, :comprises an n-type portion 1in intimate contactwith a .p-typeportion 2, both portions beingofaluminum antimonide (AlSb). The aluminumantimonideis treated in anyoftheways known in the artto makeitpor n-type. For example,p-typexmaterial may be prepared by adding astoichiometricexcessof Al tothe compound and similarly the use of excess Sb produces n-typematerial.

The p-typeportion 2 has a surface 3 adapted to receive radiation in thevisible region of the spectrum (as indicated). To realize the fullefliciency of which the device isscapable, Lprefer to provide ananti-reflecting coating 9 'upon thesurfacc 3. Such a coating mayconsist, for

. example, of a film about'0. l micron thick of. ethyl cellulose or ofvinyl polyester styrene copolymer. Portion 2 is given a thickness lessthan the minority carrier diffusion 2, 73,303 Patented Feb. 1 0, 1959length, l. e., less than /Dr in whichDrepresents the difarea contactsdistributed over the surface.

As shown inthe drawing, the power generated in the device is consumed byan electrical load resistance 7 which has its terminals connectedbyconductors 8 and 9 to the coatingszS and 6, respectively.

'The device shown in Fig. 2 is similar to'that of Fig. l and the sameparts are indicated by the same reference numerals; However, in Fig. 2the n-type layer 1 of alumi- 'num antimonide has the light-receivingsurface and is made thin, as described above.

If devices of the types shown in Figs. 1 and 2am used as photoelectriccells with modulated light signals, I prefer to insert a battery inseries with the resistance 7 in such manner as will bias the p-njunction in the reverse direction.

One example of an embodiment'like that of Fig. l is as follows: In layer2, there was an excess of Al of about 10 atoms/cmfi. In layer l,therewas an excess of Sb of about 10 atoms/cm}. For a D of 10 cmF/sec.

and 1- of 10 sec., the width of the layer 2 is about .001

inch. A suitable load resistor'7 for a surface area of about 1 sq. cm.is about ohms.

While I have described my invention in connection with specificexamples, I do not desireto be limited thereto as obvious modificationswill readily present themselves to one skilled in this art.

What I claim is:

1. As a photovoltaic solar energy converter, a p-type portion ofsemi-conductive aluminum antimonide containing about 10 atoms/cm! ofp-type producing elements and an n-type portion of semi-conductivealuminum antimonide containing about 10 atoms/cm of n-type producingele'ments in intimate contact with one another and forming a p-njunction therebetween, and

electrical connections to said pand n-type portions,one of said portionshaving a surface area, adapted to receive solar energy, the thickness ofsaid one portionunderlying said receiving surface being lessthan theminority carrier difiusion length in said one portion.

2. A solar energy converter asset forthin claim I wherein a loadimpedance providing a large poweroutput is connected across theelectrical connections to the pand n-type portions.

3. As a photovoltaic solar energy converter, a p-type portion ofsemi-conductive aluminum antimoniderand an n-type portion ofsemi-conduclive aluminum antimonide in intimate contact with one anotherand forming a pm junction therebetween, electrical connections to saidpand n-type portions, one of said portions having asurface area adaptedto receive solar energy, the thicknessofusaid one portion underlyingsaid receiving surface being less than the minority carrier diffusionlength in said one portion, and an anti-reflecting coating constitutedof an organic resin film on said receiving surface.

4. A solar energy converter asset forth in :claim 3, wherein theconnection to said one portion is a smallarea ohmic contact, andtheconnection to the other portion is a large-area ohmic contact.

(References on following page) 4 References Cited in the file of thispatent FOREIGN PATENTS v UNITED STATES PATENTS 1,057,038 France Oct. 28,1953 2,402,582 Scafi' June 25, 1946 0mm REFERENCES 2 1 0111 June 46 5Metal Industry Dec 1 1953 page 50 22,987 Buck Sept-19,1950 "um Metal Ae," August 1953, pages 11 and 28, 2,644,852 Dunlap July 7, 1953 articleby Lew 2669'63S Pfam! 4 Shockley w; Electrons and Holes in Semi-Con.2780365 ClFaPm 1957 ducton, 1). Van NM C0,, Princeton, N. 1., 1950,

1. AS A PHOTOVOLTAIC SOLAR ENERGY CONVERTER, A P-TYPE PORTION OFSEMI-CONDUCTIVE ALUMINUM ANTIMONIDE CONTAINING ABOUT 1012 ATOMS/CM.3 OFP-TYPE PRODUCING ELEMENTS AND AN N-TYPE PORTION OF SEMI-CONDUCTIVEALUMINUM ANTIMONIDE CONTAININ ABOUT 1012ATOMS/CM.3 OF N-TYPE PRODUCINGELEMENTS IN INTIMATE CONTACT WITH ONE ANOTHER AND FORMING A P-N JUNCTIONTHEREBETWEEN AND